Several types of semiconductor devices include a semiconductor body (die) and a vertical dielectric layer in the semiconductor body, that is a dielectric layer extending in a vertical direction of the semiconductor body. A vertical dielectric layer can be used as a capacitor dielectric in a capacitor or as a gate dielectric or field electrode dielectric in a MOS transistor.
To produce a dielectric layer extending in a vertical direction in a semiconductor body, it is possible to produce a trench that is subsequently filled with the desired material. However, producing a very thin layer which additionally extends deeply into the semiconductor body is difficult by using such a method since a trench having a high aspect ratio (ratio of depth to width of the trench) would have to be produced for this purpose. Such a trench having a high aspect ratio either can only be produced in a costly manner or cannot be economically produced at all above a specific aspect ratio, for example, greater than 500:1 or 1000:1.
A relatively new type of a vertical power device that is known as TEDFET (Trench Extended Drain Field-Effect Transistor) includes a drift region and a drift control region that are dielectrically insulated from one another by a drift control region dielectric. In this device, the drift control region controls a conducting channel in the drift region when the device is driven in the on state. In order to be able to control the conducting channel effectively, the thickness of the drift control zone dielectric should be as small as possible. Furthermore, it is desirable that the drift control region dielectric extends over the entire length of the drift region which extends in the vertical direction of the semiconductor body of the device.
In particular in a TEDFET operation scenarios may occur in which the electric field across the dielectric layer should be lower at some locations of the dielectric layer than at other locations. In order to prevent the dielectric layer from being damaged, the dielectric layer should be thicker at those locations where a reduced electric field across the dielectric layer is required.
There is therefore a need to provide a method for producing a semiconductor device with a vertical dielectric layer, in particular a vertical dielectric layer that has thickness that varies along the length of the dielectric layer.